[cDAC] Stack walk GC reference scanning and bug fixes (1/5) by max-charlamb · Pull Request #127395 · dotnet/runtime

max-charlamb · 2026-04-24T18:35:02Z

Summary

Part 1 of 5 stacked PRs splitting #126408 into reviewable pieces.

What this PR contains

Stack walker fixes (IsFirst preserved for skipped frames, UpdateState refactor)
PromoteCallerStack / PromoteCallerStackUsingGCRefMap for transition frames
GCRefMapDecoder + FindGCRefMap with ReadyToRun import section resolution
SOSDacImpl.GetStackReferences using cDAC contract
GCInfoDecoder.EnumerateLiveSlots goto removal
GcSignatureTypeProvider for GC type classification
Data descriptor additions (TransitionBlock, ExceptionInfo, frame types)
RequiresInstArg, IsAsyncMethod, HasRetBuffArg on IRuntimeTypeSystem

Stack overview

PR	Content	Status
→ This PR	Stack walk fixes + GC scanning	🔄
PR 2	RuntimeSignatureDecoder (ELEMENT_TYPE_INTERNAL)	Pending
PR 3	ArgIterator port from crossgen2	Pending
PR 4	Native stress framework (cdacstress.cpp)	Pending
PR 5	Managed stress tests + CI pipeline	Pending

Testing

1707/1707 unit tests pass ✅
Dump tests (StackWalkDumpTests, StackReferenceDumpTests) validate end-to-end

Note

This PR description was created with AI assistance from Copilot.

Implement GC reference scanning for stub/transition frames and fix stack walker state machine bugs: - PromoteCallerStack/PromoteCallerStackUsingGCRefMap for transition frames - GCRefMap decoder for ReadyToRun import section resolution - FindGCRefMap with FindReadyToRunModule fallback - SOSDacImpl.GetStackReferences using cDAC contract - Fix IsFirst preserved for skipped frames - Fix skipped frame handling moved to UpdateState - GCInfoDecoder goto removal (ReportUntrackedAndSucceed local function) - RequiresInstArg, IsAsyncMethod, HasRetBuffArg on IRuntimeTypeSystem - ExceptionInfo ClauseForCatch fields for catch handler detection - Data descriptor additions for frame types and TransitionBlock layout Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

dotnet-policy-service · 2026-04-24T18:36:37Z

Tagging subscribers to this area: @steveisok, @tommcdon, @dotnet/dotnet-diag
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Copilot

Pull request overview

Implements the first slice of cDAC stack-walk GC reference scanning, extending data descriptors/contracts and wiring SOSDacImpl.GetStackReferences to use the cDAC StackWalk contract (including transition-frame root scanning via GCRefMap and signature-based fallback).

Changes:

Add/extend cDAC data descriptors and contract data types for transition frames, ReadyToRun import sections, and exception clause ranges needed for stack GC root enumeration.
Refactor StackWalk filtering/state transitions and implement managed/live-slot + frame-based GC root scanning paths.
Extend contract APIs (ExecutionManager/GCInfo/RuntimeTypeSystem) and update solution/test project structure to include StressTests.

Reviewed changes

Copilot reviewed 31 out of 31 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/native/managed/cdac/tests/MockDescriptors/MockDescriptors.ExecutionManager.cs	Updates mock ReadyToRunInfo descriptor layout with import section fields.
src/native/managed/cdac/tests/Microsoft.Diagnostics.DataContractReader.Tests.csproj	Treats StressTests as a separate test project and excludes it from unit-test compilation.
src/native/managed/cdac/cdac.slnx	Adds StressTests project to the cdac solution filter.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/SOSDacImpl.cs	Implements `GetStackReferences` using cDAC StackWalk contract, with DEBUG cross-check.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/ReadyToRunInfo.cs	Reads/imports R2R import section pointer + count into the contract data.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/Frames/TransitionBlock.cs	Exposes descriptor-provided layout offsets used for GCRefMap/arg-reg scanning.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/Frames/StubDispatchFrame.cs	Adds GCRefMap + lazy-resolution fields for stub dispatch frame root scanning.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/Frames/ExternalMethodFrame.cs	New contract data type for ExternalMethodFrame GCRefMap-based scanning.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/Frames/DynamicHelperFrame.cs	New contract data type for DynamicHelperFrame flag-based scanning.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Data/ExceptionInfo.cs	Adds catch-handler clause range fields for interruptible-offset override logic.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/StackWalk_1.cs	Refactors stack-walk filtering/Next integration and adds GC root enumeration behaviors.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/GC/GcSignatureTypeProvider.cs	Adds signature-type classifier used by signature decoding for GC scanning.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/GC/GCRefMapDecoder.cs	Adds managed decoder for the compact GCRefMap bitstream.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/StackWalk/FrameHandling/FrameIterator.cs	Adds return-address retrieval and frame-type-specific GC root scanning (GCRefMap/MetaSig paths).
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/RuntimeTypeSystem_1.cs	Implements `RequiresInstArg` and `IsAsyncMethod` for TransitionFrame argument layout decisions.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/GCInfo/IGCInfoDecoder.cs	Extends decoder surface to expose interruptible ranges.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/GCInfo/GCInfo_1.cs	Plumbs `GetInterruptibleRanges` through the GCInfo contract.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/GCInfo/GCInfoDecoder.cs	Removes `goto`, fixes untracked-slot reporting behavior, and keeps decoding accessible.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/ExecutionManager/ExecutionManager_2.cs	Exposes `FindReadyToRunModule` in ExecutionManager v2 contract.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/ExecutionManager/ExecutionManager_1.cs	Exposes `FindReadyToRunModule` in ExecutionManager v1 contract.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/ExecutionManager/ExecutionManagerCore.cs	Implements R2R module resolution via RangeSection lookup.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/DataType.cs	Adds DataType entries for new frame data types.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IRuntimeTypeSystem.cs	Adds `RequiresInstArg` and `IsAsyncMethod` to abstractions interface.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IGCInfo.cs	Adds `InterruptibleRange` and `GetInterruptibleRanges` to the public abstraction contract.
src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Abstractions/Contracts/IExecutionManager.cs	Adds `FindReadyToRunModule` to the abstraction contract.
src/coreclr/vm/readytoruninfo.h	Adds cdac_data offsets for import sections in ReadyToRunInfo.
src/coreclr/vm/frames.h	Adds cdac_data for ExternalMethodFrame/DynamicHelperFrame and fields for StubDispatchFrame GCRefMap resolution.
src/coreclr/vm/datadescriptor/datadescriptor.inc	Adds/extends descriptors for new frame fields, transition block offsets, and catch clause ranges.
docs/design/datacontracts/StackWalk.md	Documents new descriptors used by stack walking + GC reference scanning.
docs/design/datacontracts/RuntimeTypeSystem.md	Documents new RuntimeTypeSystem contract methods.
docs/design/datacontracts/GCInfo.md	Documents new GCInfo contract API for interruptible ranges.

Copilot · 2026-04-24T18:39:59Z

+
+        // These are offsets relative to the TransitionBlock pointer, stored as field "offsets"
+        // in the data descriptor. They represent computed layout positions, not actual memory reads.
+        FirstGCRefMapSlot = (uint)type.Fields[nameof(FirstGCRefMapSlot)].Offset;
+        ArgumentRegistersOffset = (uint)type.Fields[nameof(ArgumentRegistersOffset)].Offset;


TransitionBlock data descriptor now defines OffsetOfArgs, but the managed TransitionBlock contract type doesn’t expose or initialize a corresponding property. This leaves the contract/data-descriptor/documentation out of sync and makes it harder for callers to consume the new layout information consistently.

Consider adding an OffsetOfArgs property (similar to FirstGCRefMapSlot/ArgumentRegistersOffset) or removing the unused descriptor/doc entry until it’s actually consumed.

This will be used in a later PR

Copilot · 2026-04-24T18:40:00Z

+    public GcTypeKind GetGenericMethodParameter(object? genericContext, int index) => GcTypeKind.Ref;
+    public GcTypeKind GetGenericTypeParameter(object? genericContext, int index) => GcTypeKind.Ref;


GetGenericTypeParameter/GetGenericMethodParameter currently classify all generic parameters as GcTypeKind.Ref. In the native implementation (MetaSig + SigTypeContext), generic parameters are resolved against the actual instantiation and can be non-GC (e.g., int, float) or value types with embedded refs. Treating them unconditionally as object refs risks reporting bogus GC roots and producing incorrect/unstable stack reference enumeration.

Consider resolving generic parameters using the method/type instantiation from IRuntimeTypeSystem (or returning GcTypeKind.Other and deferring reporting) until proper instantiation-based classification is implemented.

Suggested change

public GcTypeKind GetGenericMethodParameter(object? genericContext, int index) => GcTypeKind.Ref;

public GcTypeKind GetGenericTypeParameter(object? genericContext, int index) => GcTypeKind.Ref;

public GcTypeKind GetGenericMethodParameter(object? genericContext, int index) => GcTypeKind.Other;

public GcTypeKind GetGenericTypeParameter(object? genericContext, int index) => GcTypeKind.Other;

Copilot · 2026-04-24T18:40:00Z

+        catch (System.Exception)
+        {
+            hr = HResults.E_FAIL;


The catch block sets hr = E_FAIL for all exceptions, which drops the more specific HRESULTs typically returned elsewhere in this file (most methods use hr = ex.HResult). This can change observable behavior for callers (e.g., E_INVALIDARG, E_POINTER, E_NOTIMPL) and makes DEBUG validation against the legacy DAC less meaningful.

Consider setting hr = ex.HResult (and optionally mapping NotImplementedException/missing-contract cases to E_NOTIMPL) to keep HRESULT semantics consistent with the rest of SOSDacImpl.

Suggested change

catch (System.Exception)

{

hr = HResults.E_FAIL;

catch (System.Exception ex)

{

hr = ex.HResult;

jkotas · 2026-04-25T00:43:40Z

+
+    /// <summary>
+    /// Finds the R2R module that contains the given address.
+    /// Used by FindGCRefMap to resolve m_pZapModule when it's null.


Can we do this unconditionally and drop ZapModule from the constract? ZapModule seems to be a nice-to-have cache.

(Also, ZapModule can be renamed to Module or ReadyToRunModule. Zap is a very old codename name for crossgen/ngen that we have almost eradicated from the codebase.)

Copilot AI review requested due to automatic review settings April 24, 2026 18:35

github-actions Bot added the area-Diagnostics-coreclr label Apr 24, 2026

dotnet-policy-service Bot assigned max-charlamb Apr 24, 2026

Copilot started reviewing on behalf of max-charlamb April 24, 2026 18:35 View session

Copilot AI reviewed Apr 24, 2026

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max-charlamb marked this pull request as ready for review April 24, 2026 18:44

max-charlamb requested review from noahfalk and rcj1 April 24, 2026 18:44

jkotas reviewed Apr 25, 2026

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[cDAC] Stack walk GC reference scanning and bug fixes (1/5)#127395

[cDAC] Stack walk GC reference scanning and bug fixes (1/5)#127395
max-charlamb wants to merge 1 commit intodotnet:mainfrom
max-charlamb:cdac-stackrefs-pr1

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		public GcTypeKind GetGenericMethodParameter(object? genericContext, int index) => GcTypeKind.Ref;
		public GcTypeKind GetGenericTypeParameter(object? genericContext, int index) => GcTypeKind.Ref;

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max-charlamb commented Apr 24, 2026

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jkotas Apr 25, 2026 •

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